Server-Side Testing

Assign variations on your own server before the page renders. No client-side JavaScript for the variation, no flicker, and full control over the implementation for your development team.

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checkout.server.tsBuilt by your dev team

const a = getAssignment(evaluation, 269);
if (a.variation === 48838) {
  return renderNewCheckout();
}
return renderCheckout();

Coming soonVarify SDKs, including Next.js

What you can do with it

Experiment without flicker

The variation is decided on the server and delivered in the initial HTML, so visitors never see the original switch.

Test where client-side changes can't

Run experiments in headless setups and server-side rendered applications.

Keep the dashboard workflow

Targeting, traffic distribution, start and stop stay in the Varify dashboard. Your code creates the user, asks which variation to render and writes the tracking block.

How it works

Create a server-side experiment in the dashboard, then your development team connects two API endpoints to the existing backend logic:

Create the user

On a visitor's first request, the API returns a userId. Your system stores it in a cookie, a session or your database.

Fetch the variation

Ask which variation the user gets for an experiment. The assignment is deterministic: the same user always gets the same variation for that experiment. null means the original.

Render it and add tracking

Your backend renders the matching version and writes the returned tracking block into the HTML. Varify then triggers the tracking, respecting the user's consent status.

Full guide in the documentation →

New experiment dialog in the Varify dashboard with the Server-Side experiment type selected

Server-side results, same Varify report

Your backend picks the variation. Varify evaluates it in the same report as your client-side tests.

Goals from GA4, BigQuery, Shopify or Varify Realtime Tracking
AI Results Summary
Filter by date, device and segment
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Varify result report with the goals Conversions and Revenue: Variation 1 improves conversions by 9.49 % at 99.04 % confidence, marked significant, and revenue by 9.73 % at 94.28 %, not yet significant

AvailabilityGrowthProEnterprise

Server-side testing — — ✓

Client-side testing ✓ ✓ ✓

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Frequently asked questions

Do I still need the Varify snippet?

Yes, for results. The server decides and renders the variation, but Varify must be on the page to read the tracking block in your HTML and trigger the tracking, even if varify.js plays no other part in the experiment.

What happens if I skip the tracking block?

The dashboard then shows only the experiment configuration and no results, because the delivery API has no endpoint for reporting events.

Is there an API reference for developers?

Yes. The full OpenAPI 3.1 reference with every endpoint, parameter and error code is at app.varify.io/ss/docs.

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